The molecular mechanism by which mink cell focus-inducing viruses (MCF's) induce leukemia in AKR mice is unknown. My work demonstrates that at least four regions of the viral genome control the oncogenic potential of MCF 247, the prototype of this kind of virus. This proposal will be focused on the viral genes which control the oncogenic potential of MCF 247 and on the events which occur in vivo after viruses are injected into AKR mice. A basic hypothesis will be tested. Namely, that a number of viral genes are required in the genome of the virus which is the proximal leukemogenic agent. Specific Objectives: (1) To determine if the integrase activity at the 3' end of the pol gene is important to the leukemogenic phenotype of MCF 247, recombinants between MCF 247 and Akv will be constructed, and cloned. The pathogenesis of the recombinants will be determined. (2) A similar strategy will be used to define the oncogenic importance of the gag genes (p 30, p 10). (3,4) The events which occur after recombinant viruses are injected into newborn AKR and NFS mice will be defined by tracking viruses which have a molecular tag in the long terminal repeat (LTR). The genomes of proviruses containing the tag will be defined by Southern blotting and molecular cloning. The nature of the proviruses and their location in the DNA of preleukemic T cells and tumors will be determined. (5) To assess the role of the envelope proteins in leukemogenesis, the oncogenic potential of a moleculary-constructed defective retrovirus derived from MCF 247 will be determined. The defective virus, packaged into helper-free viral particles by the 2 cell line, will be used to infect AKR bone marrow. Pluripotent stem cells (i.e. CFU-S) will be isolated from histocompatible lethally irradiated recipients engrafted with the virus infected marrow. The pathogenesis resulting from the infusion of a single virus infected CFU-S into a secondary sublethally irradiated recipient will be determined. These studies should identify the viral genes involved in oncogenesis, describe the early recombination steps which occur after viruses are injected into mice, and determine if these events are important to leukemogenesis by MCF viruses.